The present invention relates to a process for decontaminating inert substrate materials such as soils, sludges, sediments, drilling mud and cuttings, spent activated carbon, and wood. More particularly, the invention concerns an improved process and apparatus for thermally separating mercury and organic contaminants such as hydrocarbons, polychlorinated biphenyls (PCB""s), pentachlorophenols (PCP""s), polyaromatic hydrocarbons (PAH""s), insecticides, herbicides, creosote, pesticides, dioxins and furans. The removed contaminants are removed as vapour without employing combustion, are collected and condensed for further treatment and recovery.
Increasing attention has been paid to public health consequences of introducing industrial wastes, such as halogenated and non-halogenated organic compounds into the environment. As this attention has increased, governmental regulations have also been put in place to mandate the removal of these compounds to maximum permissible residual levels in the soils and other matrices of former disposal sites.
Traditionally, clean-up of disposal sites involved the procedure of removing contaminated soil or material to a designated secure land fill area. However, the number and volume of designated land fill areas has been greatly reduced and therefore a growing need to sanitize soils, and other matrices, with an efficient and economical treatment process is required.
In response to this need, portable incineration systems have been proposed, for example, U.S. Pat. No. 4,667,609 discloses a mobile apparatus for infrared heating of soils contaminated by various hydrocarbons. However, in incineration systems such as this the heating step is carried out to the point of complete combustion. Hence, operation of such a system would likely be precluded by governmental regulations which are extremely stringent with respect to the output of gases and the like from incineration systems.
An alternative to incineration is taught by U.S. Pat. No. 4,864,942 which discloses a method for removing organic compounds such as PCB""s from soils by volatizing the organic compounds at temperatures well below what would be defined as xe2x80x9cincinerationxe2x80x9d. Generally speaking, these temperatures would not exceed 1200xc2x0 F.
However, the time periods necessary for treatment to effect complete volatilization of contaminants, without combustion, are extremely slow and may well be an hour or more and in the case of mercury highly unlikely.
Accordingly, there is a need for an apparatus which can maximize the heat transfer to the substrate to be treated so as to minimize treatment time. Furthermore, thermal expansion of treatment chambers may also be a problem and there is therefore a need for a treatment chamber which can preferably respond to varying temperatures of the treatment process.
In a broader embodiment of the process according to the present invention, contaminants are separated from inert substrate materials such as soils, sludges, sediments and drilling muds and cuttings by a process that subjects inert materials contaminated with mercury or an organic compound to a temperature effective to volatilize the contaminants but below combustion temperature, with continuous removal, collection, condensation of all the vapours, for a period of time sufficient to effect the desired degree of contamination removal from the inert material and prevent the release of contaminated emissions.
When applying the inventive process and apparatus to decontaminate a large amount of material, the process is preferably carried out with an indirectly heated air tight extraction chamber consisting of a suspended double troughed chamber equipped with rotating augers which maximizes the heat transfer and minimizes dust to the substrate while eliminating difficulties caused by thermal expansion of prior art chambers.
Temperatures are controlled to keep the average soil temperature of material being processed at or below 600xc2x0 C. to 650xc2x0 C. to ensure high removal efficiencies. At these temperatures the volatilization component of the contaminated substrate vapourizes to form a vapour phase, leaving behind an inert solid phase. The vapour phase, which contains few fine solid particles, steam, air and vapourized contaminants such as hydrocarbons and PCB""s, is continuously drawn off from the chamber and is subsequently collected, condensed and recovered for recycling or disposal by appropriate procedures.
Accordingly, the invention comprises an apparatus for separating contaminants form inert substrate materials, comprising an essentially suspended air-tight processing chamber having a substrate inlet and a substrate outlet, said chamber having two or more channels for processing of the substrate, a means for indirectly heating the chamber, a means for moving substrate through the two or more troughs of the chamber from the substrate inlet to the substrate outlet, and a vapour condensate handling system for removing and condensing vapours from the chamber to remove and recover contaminants.
The invention further comprises a method for separating mercury and organic contaminants from contaminated inert substrate materials comprising the steps of feeding inert solid material contaminated with mercury and/or organic compounds into a suspended treatment chamber heated externally with a heating means to such a temperature that the mercury and organic compounds are volatilized, moving said material through the chamber in a manner which exposes a maximum surface area of the inert solid material to the indirect heat within the chamber to assist in the rapid heating and processing of the material, removing the solids free of contaminants from the chamber, removing the vapour phase constituents from the chamber and conducting to a means for condensation and recovery of contaminants.